The invention relates in general to coordinate measurement machines (CMMs) and in particular to a method and system for assisting a user taking measurements using a CMM.
The manufacturing/industrial marketplace took on a new face during the 1980's with the introduction of computer-aided design (CAD) and computer-aided manufacturing (CAM). While CAD allowed engineers to produce 3-D images in the front end of the design process, which shortened the production cycle and led to tremendous gains in productivity, CAM software and equipment increased the efficiency and quality of machined single parts. In essence, these new technologies revolutionized the marketplace by increasing productivity, improving quality, and reducing costs. Despite these technological advances in design and manufacturing, something important was missing from the production cycle: a highly accurate, efficient, and convenient measurement methodology for ensuring that the products and components—both on and off the production line—met the original CAD specifications. The design process, with the help of CAD, had become innovative and sophisticated; so too, had the machining process through CAM. Yet measuring the assemblies made of these parts against the CAD model, for the most part, has continued to remain unwieldy, expensive, and unreliable.
Traditionally, the measurement and quality inspection function in the manufacturing process has been time-consuming and limited in size, scope, and effectiveness for a number of reasons. Manual measurement tools, such as calipers and scales may be slow, imprecise, and always one-dimensional. Analog test fixtures are costly and inflexible. And standard stationary CMMs while providing a high degree of precision, are generally located in quality control labs or inspection departments at a distance from the manufacturing floor. Parts must be removed one at a time and transported to the lab for inspection. As a result, CMMs measure only small, readily-moved subassemblies and components—which often translates into significant “down time” for the production line. In essence, traditional measurement techniques—also known as metrology—have lagged far behind in the technological advance of the production process.
The CAD/CAM and metrology markets, as well as a worldwide emphasis on quality in all aspects of the manufacturing process, are driving the need for an extension of the CAD/CAM techniques, which the inventor refers to as computer-aided manufacturing measurement. Computer-aided manufacturing measurement is CAD-based total quality assurance technology. This last phase of the CAD revolution has remained incomplete because of the significant technical demands for adaptive measurement hardware and usable CAD-based measurement software for the difficult manufacturing environment. Computer-aided manufacturing measurement takes conventional metrology from a single-parts-only, high-level precision testing methodology—behind the door of the quality control lab—to a whole products, intermediate-level precision measurement system at every step of the manufacturing process—at any location on the factory floor. Measurements of part dimensions and/or characteristics may be made on the production floor to determine compliance with specifications and ensure quality.
FIG. 1 is a diagrammatic view of a conventional, portable CMM 10 comprised of a manually operated multi-jointed arm 12 and a support base or post 14, a serial box 16 and a host computer 18. It will be appreciated that arm 12 electronically communicates with serial box 16 which, in turn, electronically communicates with host computer 18. Additional detail of the conventional three-dimensional measuring system can be found in U.S. Pat. No. 5,402,582, the contents of which are incorporated herein by reference.
An improvement to the three dimensional coordinate measuring system of FIG. 1 is described in U.S. Pat. No. 5,978,748, the contents of which are incorporated herein by reference. This patent discloses a system in which a controller is mounted to the arm and runs an executable program which directs the user through a process such as an inspection procedure. In such a system, a host computer may be used to generate the executable program. The controller mounted to the arm is used to run the executable program but cannot be used to create executable programs or modify executable programs. By way of analogy to video gaming systems, the host computer serves as the platform for writing or modifying a video game and the arm mounted controller serves as the platform for playing a video game. The controller (e.g., player) cannot modify the executable program. As described in U.S. Pat. No. 5,978,748, this results in a lower cost three dimensional coordinate measurement system by eliminating the need for a host computer for each articulated arm.
A coordinate measurement system application may perform operations against CAD models to compare the actual part being measured to the nominal CAD values. Since CAD models may be generated in numerous formats that are unique from vendor to vendor and sometimes protected by encryption, translation from one format to another is difficult, unreliable, time consuming and/or costly. The majority of the market is currently dominated by at least six CAD formats. In the normal course of performing operations, CAD data must be translated from its original CAD format to the coordinate measurement system application and stored internally in its disassociated format. This process requires translation of the data. Translation of data often results in certain data imperfections, and may not be possible at all due to translator idiosyncrasies and changes in CAD engine formats. Such a result is undesirable because the translated data may be unreliable and unusable.
This problem has been addressed through the creation of specific coordinate measurement system applications that integrate into the CAD engine. Although this may address the translation issues, it creates a problem because a software provider is forced to serve only the users of the particular CAD engine, or to rely on translators written for the specific CAD engine. In the later instance, the translation problem is again an issue.
There is a need, therefore, for a method and system for a CAD engine independent tool for users of coordinate measurement systems. Such a method and system would render the coordinate measurement system more versatile and readily adaptable to computer-aided manufacturing measurement.